Page 20 - Differential Diagnosis in Small Animal Cytology, The Skin and Subcutis

Choice and Correct Use of the Microscope

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For the routine clinical microscope, an Abbe 0.9 is considered adequate and is normally present
on most standard microscopes. More advanced microscopes with fluorite objectives usually
VetBooks.ir carry a higher-corrected condenser.

Microscope illumination
For a very long time, microscopes were equipped with tungsten–halogen filament lamps. The
only disadvantage of these lamps was the short lifespan caused by the high temperatures reached
when in use. Over the past few years, microscopes have moved to LED illumination, giving a
bright white light without heat dissipation. However, the colour characteristics of LED lights are
not directly comparable to halogen lights, especially with earlier LED illumination. For this rea-
son, an adaptation time is recommended when changing from halogen to LED lighting, as the
appearance of some stains may look different depending on the light source.

1.3 Setting up a Microscope

There is only one way a microscope should be set up for any given objective. Deviating from this will only
reduced the quality of the image. When setting up a microscope it is important to carry out the following:

• Position the condenser to the correct height and centration in relation to the objective.
• Ensure that the diaphragm (or diaphragms) on the microscope is correctly set (see later).
Eyepieces

Often overlooked, the eyepieces need to be correctly set or eyestrain will occur. Most microscopes
have one eyepiece with a focusing capability and markings showing + and – dioptre settings.

Procedure
• Focus on a specimen looking through the fixed, non-adjustable eyepiece.
• Looking through the adjustable eyepiece, rotate this until the focus is reached (sharp image).

Illumination
• Koehler illumination

Procedure
• Place a slide with a good contrast specimen on the stage and use the 10× objective. Focus
on the specimen with the focus controls.
• Move the condenser using the condenser rack and pinion controls under the stage until
it is about 0.5 cm from the top.
• Close the field diaphragm. At this point the leaves of the diaphragm (which may not be
in the centre of the field) will become visible.
• Move the condenser up and down until the leaves are in focus.
• Use a knurled screw or Allen key (usually in the front of the condenser mount, at the left
or right) to centre the image of the diaphragm.
• Open the field diaphragm until it is just out of the field of view.
In this way the condenser will be at the correct height and centred in the optical pathway, allowing
the best illumination of the specimen to achieve the best possible image quality.